PHP Help

I’m trying to change the template php file but I don’t understand the code – can anyone explain what this means please? All I want to do is change the file so a border is displayed instead of an image the coke is

<?php $_F=__FILE__;$_X='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';eval(base64_decode('JF9YPWJhc2U2NF9kZWNvZGUoJF9YKTskX1g9c3RydHIoJF9YLCcxMjM0NTZhb3VpZScsJ2FvdWllMTIzNDU2Jyk7JF9SPWVyZWdfcmVwbGFjZSgnX19GSUxFX18nLCInIi4kX0YuIiciLCRfWCk7ZXZhbCgkX1IpOyRfUj0wOyRfWD0wOw=='));?>